The semiconductor integrated circuit industry has experienced rapid growth in the past several decades. Technological advances in semiconductor materials and design have produced increasingly smaller and more complex circuits. These material and design advances have been made possible as the technologies related to processing and manufacturing have also undergone technical advances. In the course of semiconductor evolution, the number of interconnected devices per unit of area has increased as the size of the smallest component that can be reliably created has decreased.
One broad category of commonly used techniques employed to form material layers and alter properties over semiconductor wafers is deposition, which includes the techniques such as chemical vapor deposition, physical vapor deposition, sputtering, ion implantation, etc. In many kinds of deposition, a plasma is used to accelerate ions or other particulars toward the surface of a wafer undergoing the deposition process. For example, in sputtering an ion of a noble gas may be used to facilitate forceful collisions with a target. Atoms of the target are knocked free by the colliding ions and then condense on the exposed surface of a semiconductor wafer forming a thin layer or film of the target material. In an ion implantation process, the ions may be distributed in a plasma generated above the surface of the wafer. The ions may then be accelerated toward the wafer by the manipulation of a charge or power applied to the wafer or to a wafer support device.
Particularly as the size of wafers used in the semiconductor integrated circuit industry has increased, existing techniques have been found to be unsatisfactory in terms of producing a uniform layer on the semiconductor wafer.
These figures will be better understood by reference to the following detailed description.